Method of making a core drill and the like



April 29, 1958 H. F. BRINKER ETAL 2,832,238

METHOD OF MAKING A CORE DRILL AND THE LIKE Original Filed Sept. 29, 1950Fll3-1- lawentors: fine/er fflE/A/A [E and MuwMJ/Qm M United StatesPatent 2,832,238 METHOD OF MAKING A CORE DRILL AND THE LIKE Harry F.Brinker, Whitaker, and William J. Flynn, Braddock, Pa.

Original application September 29, 1950, Serial No. 187,526. Divided andthis application September 2, 1953, Serial No. 378,118

2 Claims. (Cl. 76-108) have been proposed. While core drills madeaccording to prior art methods have been effected to a degree, they havenot been entirely satisfactory particularly when it was sought to outlong cores out of hard material, such as water-hardened armor platesteel. When subjected to such difficult use, the cutting bits of thedrills, which were usually made of hard and brittle material, such astungsten carbide, would tend to shatter and spall.

It is, accordingly, a primary object of our invention to provide amethod of making a core drill of improved composition of material havinga design which adapts it to the drilling of hard material.

Another object of our invention is to provide a method of making a coredrill wherein metal cutting bits are deposited and fused on a helicallyfluted body of steel and annealed.

These and other objects will become more apparent after referring to thefollowing specification and attached drawing, in which:

Figure 1 is a plan view of the finished drill;

Figure 2 is a side elevational view showing the drill during the firststage of processing;

Figure 3 is a top plan view of Figure 2;

Figure 4 is a view similar to Figure 2 showing the drill during thesecond stage of processing;

Figure 5 is a top plan view of Figure 4;

Figure 6 is a side elevational view of the finished drill; and

Figure 7 is a top plan view of Figure 6.

Referring more particularly to the drawing, reference numeral 2indicates an elongated cylindrical or tubular body having a shank 4 atone end and a plurality of circumferentially spaced cutting bits 6 atthe other end. Shank 4 and the cutting bits 6 are integral with the body2. A shoulder 8 surrounds the tubular body at the bottom of the shank 4and a center bore 10 extends coaxially through the shank and through thetubular body. The outer periphery of the body 2 is provided with threehelical external flutes 12 which extend away from the cutting end of thetool with spaced lands 14 therebetween. Each of the flutes 12 has twowalls 16. At one end, the lands 14 are ground to terminate in a helicalsurface 18 on the cutting end of the tool. The

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cutting bits 6, which are made of electrically deposited and fusedhigh-speed steel which will be described more fully hereinafter, areintegral with the body 2 and are formed I by the intersections ofhelical surfaces 18 with the walls 16 of the flutes. The bit surfaces 20that ,are formed by the walls 16 lie substantially in the same plane asthe axis of the tubular body 2. The cutting edges 22, which are formedby the intersections of the helical surfaces 13 and the bit surfaces 20,are normal to the axis of the tubular body 2. Thus, the cutting bits 6have neither axial nor radial rake. The total elimination of rake aspracticed in the present invention is contrary to the teachings of theprior art wherein it was universally taught that a positive or negativerake was an essential prerequisite in the manufacture of a core drill.

Three longitudinal grooves 24 may be spaced around the inner surface ofthe bore 10 for supplying coolant fluid to the cutting end of thetubular body.

The body 2 with shank portion 4 of the present invention is machinedpreferably of a low-carbon steel, such as SAE 1020 fine-grained steel,to the shape shown in Figures 2 and 3; carburized at 900 C. for 24hours; oilquenched to room temperature; heated to 780 C. in 25 to 30minutes after which approximately one inch of the cutting end is waterquenched to room temperature; the piece is then drawn at 180 to 200 C.for one hour.

The cutting bits 6 are then formed by the grinding of seats 26 in theend of the cylindrical body 2 and filling them with a high-speed steel28 deposited by the conventional arc welding process or other processwhich produces a similar result of melt welding of the highspeed steel.It has been found preferable, for the arc welding process, to use coatedelectrodes composed of steel containing substantially 18% tungsten, 4%chromium, 1% vanadium, and other alloying elements common to this gradeof steel. The conventional arc welding process has been foundsatisfactory. Metal deposition by means of an electric arc is preferablealthough deposition of the metal may be accomplished by means of a gasweld if desired. After the high-speed steel has been electrically or gasweld deposited, it is heated by means of an oxyacetylene torch or thelike to incipient fusion, which is manifest in a smoothing of theoriginal deposited metal, and cooled instill air. Omission of thisfusion treatment causes a coarse grain structure which results in thedevelopment of an undesirable hardness distribution throughout thecross-section of the bits and resultant destruction of the bits after arelatively short use. The final step consists of grinding the tool tothe shape shown in Figures 6 and 7.

Core drills made according to the present invention exhibit anexceptional resistance to wear in. the drilling of hardened materials,such as armor plate steel, and possess excellent cutting properties.

While one embodiment of our invention has been shown and described, itwill be apparent that other adaptations and modifications may be madewithout departing from the scope of the following claims.

We claim:

1. In a method of forming cutting bits on a metal tool the stepsincluding removing stock from a portion of said tool to form cutting bitseats, then depositing highspeed steel directly on said seats by meltwelding of said steel, and then, after solidification of the weldedhighspeed steel, reheating said welded high-speed steel substantially tofusion temperature.

2. In a method of forming cutting 'bits on a core 4 drill having a,cutting end, and a body formed with a References Cited in the file ofthis patent plurality of helical external flutes with lands therebevUNITED STATES PATENTS tween extending away from said cuttlng end, thesteps including removing stock from the lands adjacent said 1,803,875 fy y 5, 1931 cutting end to form cutting bit seats, then depositing high-5 1,855330 ZHPIIH P 26, 1932 speed steel directly on said seats by meltwelding of said 2,524,570 PP 3, 1950 steel, and then, aftersolidification of said welded highspeed steel, reheating the Weldedhigh-speed steel sub- FOREIGN PATENTS stantially to fusion temperature.625,459 France Apr. 23, 1950 U S DEPARTMENT OF COMMERCE PATENT OFFICECERTIFICATE OF CORRECTION April. 29, 1958 ied that error appears in theprinted specification tion and that the said Letters Patent No.2,832,238 Harry F. Brinker et al.

Column 1, line 26, for "effected" read --effective--.

Signed and sealed this let day of July 1958.

(SEAL) Attest:

KARL H. AXLINE ROBERT C WATSON Commissioner of Patents Attesting Officer

